Catalytic domain of Cyclin-Dependent protein Kinase Like Serine/Threonine Kinases. Serine/Threonine Kinases (STKs), Cyclin-dependent protein kinase like (CDKL) subfamily, catalytic (c) domain. STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. The CDKL subfamily is part of a larger superfamily that includes the catalytic domains of other protein STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase. CDKs belong to a large family of STKs that are regulated by their cognate cyclins. Together, they are involved in the control of cell-cycle progression, transcription, and neuronal function. This subfamily is composed of CDKL1-5 and similar proteins. Some CDKLs, like CDKL1 and CDKL3, may be implicated in transformation and others, like CDKL3 and CDKL5, are associated with mental retardation when impaired. CDKL2 plays a role in learning and memory.